1. Field of the Invention
This invention relates to tripod type constant velocity joint.
2. Description of the Prior Art
A conventional tripod type constant velocity joint will be described with reference to FIGS. 1 to 7.
In FIG. 1 symbol H is a cup-shaped housing and symbol S is a shaft. Numeral 1 is a trunnion mounted on the shaft. Symbol R is a spherical roller fitted to the trunnion 1 by a needle 2. Numeral 3 is a stopper and numeral 5 is a support ring. Formed in the housing H are three pairs of grooves 4 extending to an axial direction. The spherical roller R is moved slidably on a cylindrical surface 4a of the groove 4. Mounted between the housing H and the shaft S is a boot which is not illustrated.
Under the aforesaid construction, an axial movement and angular movement of the housing H and the shaft S respectively is feasible at the time when the roller R is moved slidably on the cylindrical surface 4a of the groove 4. A torque transmission in a rotation direction is feasible between the roller R and the groove 4.
Further, when the roller R is moved with a certain joint angle, a contact condition between the spherical roller R and the cylindrical surface of the groove is always constant even for an eccentric movement of the joint, because the roller R is spherical.
In such a constant velocity joint, when the roller R is rolled by torque with a certain joint angle, it is known that an axial force occurs three times per revolution on the shaft S. The cycle of axial force is increased or decreased by the influence of joint angle, torque transmission on the like. Particularly, it occurs frequently in recent high power vehicles. Further, in the event the cycle of axial force corresponds to that of a proper shaking of a vehicle body, suspension or the like and there occurs a large axial force enough to invite resonance of the vehicle body, the inconvenience is that a crew in a vehicle feels unconfortable lateral shaking. From the viewpoint of a vehicle design, the inconvenience is that the joint angle must be limited to a relatively small one.
To solve such inconvenience, a proposal has been made in UK Patent Application GB No. 2,106,219A. In this reference there are disclosed strip-like members similar to aligning members of this invention. According to this reference, the strip-like members are fixed in the axial sense to the innner component and slidable in the axial direction on the guide groove walls of the outer component. Since a portion of the strip-like member is positioned between the outer component and the spherical roller, and becomes a part of transmitting a driving force, a large pressure is applied to the strip-like members. Further, axial load fluctuation which occurs periodically is buffered by the strip-like members and maintain equilibrium within the interior of the joint.
A relative axial displacement of the strip-like members and the outer element becomes a slide, so that the most remarkable feature of a slide and tripod type constant velocity joint is that a friction resistance in a slide direction that is small is lost. That is, the spherical roller is rolled in the guide groove of the outer component. Accordingly, the disadvantage is that friction coefficient is remarkably increased and slide resistance becomes very large.
This invention aims at solving the problems of the aforesaid conventional techniques. More particularly, this invention provides a novel tripod type constant velocity joint which enables to reduce an axial force and prevent resonance of a vehicle body due to the axial force by analyzing the factors for causing the axial force as well as the influence on the axial force.
The result of my analysis is that the axial force is caused by the following three friction resistances; a friction resistance f.sub.1 acted on the trunnion 1 when the spherical roller R performs its rolling movement, a friction resistance f.sub.2 of the roller R to the groove 4 in the case of the former slides in the axial direction of the trunnion 1, and a friction resistance f.sub.3 of the roller R to the trunnion 1 (needle 2) when the roller R slides in the axial direction of the trunnion 1. It has been found that the axial force due to the friction resistances f.sub.2 and f.sub.3 is large. FIG. 7 shows the results of my analysis on the influence of occurrence of the axial force.
The mechanism of occurrence of the axial force will be described with reference to FIGS. 4 to 7.
FIG. 4 shows the condition of a relative displacement of the roller R at the movement time of the joint relative to the groove 4.
When the roller R moves from a zone [I] to a zone [II] along the cylindrical surface 4a of the groove 4, it is inclined to roll within the zone [I] in an external direction of the groove 4 by the friction resistances f.sub.2, f.sub.3 within the zone [I], but within the zone [II] in an internal direction thereof by the same friction resistances f.sub.2, f.sub.3. However, since the roller R is moved being guided along the cylindrical surface 4a of the groove 4, the external force to be balanced with the friction resistances f.sub.2, f.sub.3 is imposed on the roller R. In FIG. 4, .theta. is a joint angle, and K s a rotational surface of the trunnion 1.
It is considered that the external force occurs when a contact point of the cylindrical surface 4a and the roller R is displaced.
In the case the roller R is disposed in the zone [I] as shown in FIG. 4, the contact point A is displaced to a position B as shown in FIG. 5, thereby a component of force Ft of load FA occurs. The component of force Ft is, as shown in FIG. 6, divided into a component of force Ft cos .theta. to be balanced with the sum of the friction resistances f.sub.2 and f.sub.3 and a component of force Ft sin .theta. in a direction of the shaft S. Addition of the component of force Ft sin .theta. in the shaft direction to the friction resistance f.sub.1 appears as the axial force. When the spherical roller R is positioned on a border of the zones [I] and [II] (the position of 90 degree movement of the joint), sin .theta. is equal to zero. (sin .theta.=0). Accordingly, the component of force Ft sin .theta. in the axial direction becomes zero, and only the friction resistance f.sub.1 appears as axial force. This is a phenomenon of the trunnion 1A, one of three trunnions 1A, 1B and 1C. With regard to the other two trunnions 1B, 1C, respectively, the joint rotational angle is displaced by 120.degree.. Accordingly, the axial force appeared on the shaft S is the sum of respective axial forces of the trunnions 1A, 1B and 1C as shown in FIG. 7. Since a force direction of a compression force and of a tensile force is opposing to each other, its difference becomes a resultant axial force.
As described above, my analysis on mechanism of occurrence of the axial force and the influence on the axial force has resulted in that it is required to reduce the friction resistances f.sub.1, f.sub.2 and f.sub.3 in order to solve the problems of the conventional constant velocity joint. However, since the friction resistance f.sub.1 becomes small by movement, it is required to reduce the friction resistances f2, f3, that is, the component of force Ft sin .theta. in a direction of the shaft S. The reason why the component of force Ft sin .theta. occurs might be due to that since the groove 4 has the cylindrical surface 4a as shown in FIGS. 4 to 7 and the surface of the spherical roller R is spherical, in case of joint angle .theta. (.theta.&gt;0) a contact point of the cylindrical surface 4a and the spherical roller R is displaced out of the plane (rotational surface of the trunnion) including the axial lines of the three trunnions, and a direction of force Ft occurred on the contact point is intersected with the rotational surface K.